login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A320446 Covers of triangles by tetrahedra: number of labeled 4-uniform hypergraphs spanning n vertices such that every three vertices appear together in some edge. 0
1, 1, 1, 0, 1, 6, 5789 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

LINKS

Table of n, a(n) for n=0..6.

EXAMPLE

The a(5) = 6 hypergraphs:

  {{1234},{1235},{1245},{1345}}

  {{1234},{1235},{1245},{2345}}

  {{1234},{1235},{1345},{2345}}

  {{1234},{1245},{1345},{2345}}

  {{1235},{1245},{1345},{2345}}

  {{1234},{1235},{1245},{1345},{2345}}

MATHEMATICA

Table[Length[Select[Subsets[Subsets[Range[n], {4}]], Length[Union@@(Subsets[#, {3}]&/@#)]==Binomial[n, 3]&]], {n, 6}]

CROSSREFS

Cf. A006126, A038041, A299471, A301922, A302374, A302394, A306021, A319540, A320395, A322451.

Sequence in context: A116117 A116135 A011788 * A172649 A111152 A202969

Adjacent sequences:  A320443 A320444 A320445 * A320447 A320448 A320449

KEYWORD

nonn,more

AUTHOR

Gus Wiseman, Jan 10 2019

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 25 20:58 EDT 2020. Contains 334597 sequences. (Running on oeis4.)